This project raised a question for me: what is the copyright or licensing situation with Google’s Material Design? The specification itself appears to be copyright Google, but several implementations of the specification on the Web are under permissive licenses:

Google’s Web Starter Kit (https://developers.google.com/web/starter-kit/) uses the Apache License 2.0

Polymer is implementing Material Design for its Paper Elements collection (https://www.polymer-project.org/docs/elements/paper-elements...) under a BSD license.

Angular is implementing it (https://material.angularjs.org/) under the MIT license.

Is Material Design for Google and Android apps only? Can anyone implement it on the Web?